While the 6 th edition of the NSSS, which was published in , contained several important updates compared to its predecessor, including the introduction of Building Information Modelling BIM for the first time, it was always viewed by its authors as an interim version, pending a comprehensive review. This interim status is reflected in the fact that the 6 th edition was only available as a PDF document. The resulting 7 th edition contains several significant changes from the 6 th edition, as summarised below:.
ISO has been around for a while and its use is common in the world of highway and railway bridges, where welds have to cope with the demands of dynamic loading and the consequences of failure could be fatal. However, it was not seen as necessary in the more benign environment of a standard steel framed shed where the loads are generally static in nature and the consequences of failure are less severe.
It is worth noting that the change in status only applies to the NSSS; the rules in EN remain unchanged, so there are currently no implications for CE marking.
There are no requirements for EXC 1 at present. For EXC 2 and above, the frame manufacturers will need to have a Weld Quality Management System WQMS that complies with the requirements of ISO across a range of areas including welding personnel and their training, equipment, welding procedures, consumables, heat treatment, inspection and testing, corrective actions for non-conformance and identification and traceability.
The ISO WQMS should be very similar to the existing welding procedures already required for CE marking, so no major changes are anticipated, subject to the comments in the next section. The main issue for frame manufacturers is the need for additional certification and the availability of this certification service. Frame manufacturers will need to check whether the Notified Body that they currently use for CE marking is also accredited for ISO certification.
In addition to mandatory certification to ISO , other changes have been made to the sections of the NSSS dealing with welding and weld testing.
Firstly, in the context of training welding operatives and ensuring that they hold the appropriate qualifications, the RWC may now act as the examiner, avoiding the need to appoint the services of an external examiner.
This is in line with EN and will be welcome news for small fabricators and frame manufacturers. CE Marking version: October The British Constructional Steelwork Association is the national organisation for the constructional steelwork industry.
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This document Newer versions Older versions. British Constructional Steelwork Association The British Constructional Steelwork Association is the national organisation for the constructional steelwork industry. Find out more. Typical codes are:. The mechanical properties of strip steel used in construction are given in BS EN [14]. In addition, BS EN [15] is the standard for tolerances on dimensions and shape for continuously hot-dip coated steel sheet and strip used in structural applications.
A typical code for purlins is:. For steel members and components, the designer will specify the steel grade typically S or S and sub-grade. Guidance on selection of sub-grade for toughness against brittle fracture for building steelwork is given in SCI ED for buildings where fatigue is a design consideration and SCI publication P for buildings where fatigue is not a design consideration. Further general guidance on steel product standards is given in Guidance Note 3.
In buildings, fasteners will usually be non-preloaded bolts , property class 8. Product standards for fastener assemblies are summarized in the NSSS. The majority of building steelwork contractors have access to numerically controlled machines for cutting and drilling , often combined in 'saw and drill lines' and other fabrication processes.
Small details such as notching may be carried out manually or with the use of CNC controlled machines. The accuracy of numerically controlled fabrication is very high - for example a saw is accurate to a fraction of a millimetre for length and 0. Similarly, the requirements for thermally cut edges are met with modern equipment. All fabricated items are required to be marked with a unique identifier and this is normal practice in fabricating factories. The identifier ensures traceability to inspection and testing documents.
Welds are generally specified on drawings by symbols in accordance with the relevant standard. Welding is a relatively expensive operation and weld sizes should not be over-specified.
Welding is also a specialist activity and should be executed by appropriately qualified, trained and experienced personnel.
Furthermore, the NSSS requires that the steelwork contractor's system for the management of welding will meet:. All welds must be inspected , and a proportion of them should be tested as prescribed in the NSSS. The adherence to the reference standards should ensure that the welding is completed without defects in the welds.
It is now mandatory for the welding of shear studs to be performed in accordance with the requirements and procedures of BS EN ISO [16]. The connection designer for building steelwork will often select one particular size of bolt, typically a M20 x 60 fully threaded, non-preloaded property class 8.
Preloaded bolts are selected only when the avoidance of slip in service is necessary. They are more expensive and involve additional cost in fabrication and on site.
A new clause has been added in the 7th Edition Clause The erected steelwork must be within certain tolerances on position and straightness so that the steel can be properly assembled on site, that other building components can be properly constructed on and around the steel frame and that the design assumptions are realised.
These deviations are typically given for fixed points, such as the level where beams connect to columns. The deflections due to loading are not covered by tolerances ; if the deflected position is critically important, it is invariably better to make provision for adjustment.
The specification of cost-effective protective treatments for structural steelwork should be relatively straightforward for most common applications as long as the factors that affect durability are appreciated. The optimum protection treatment combines good surface preparation with suitable coating materials for a required durability at a minimum cost.
Modern practices applied according to the relevant industry standards provide an opportunity to achieve the desired protection requirements for specific structures.
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